Understanding the structure and properties of geological formations can reduce the cost of drilling wells for oil and gas exploration. Measurements made in a borehole (i.e., down hole measurements) are typically performed to attain this understanding, to identify the composition and distribution of material that surrounds the measurement device down hole.
A walk-away vertical seismic profile (VSP) survey includes some of these measurements. This type of survey is used to determine the response of a plurality of receivers in a borehole to excitation by at least one seismic source located at a plurality of distances from the well-bore. However, the results are often affected by seismic anisotropy, which induces a directional dependence in wave propagation. For example, in an anisotropic Earth model, seismic velocity can vary with the ray path propagation angle. This is caused by the alignment of rock heterogeneities, including velocity layering, crystal fabrics, fractures, and other microstructures. Thus, the determination of anisotropic parameters from surface seismic data is often difficult, due to relatively poor data quality and the relatively low frequencies at which the measurements are made.